Hitherto, there can be found two kinds of uses in a rust inhibitor, one is use of same to provide rust preventing effect to a lubricant such as turbine oil, engine oil, gear oil or hydraulic fluid and the other is use of same as an ingredient in so-called rust preventive oils which prevent rusting of a metallic product.
Primary properties required in these inhibitors are to have enough solubility to a mineral oil used and to adsorb to a metal surface strongly to prevent water, salts, corrosive gases (NOx, SOx) and dust from attacking chemically on metal surface which cause rusting.
In the past, organocarboxylic acids, salts or esters thereof, sulfonates, amines, phosphoric acid and salts or esters thereof have been well-known as a rust inhibitor. As an industrial lubricant organocarboxylic acids, especially alkenyl succinic acid and esters thereof have been primarily used. And as a rust preventive oil organocarboxylic acid esters have typically been used.
The alkenyl succinic acid and its derivatives have been apt to interfere with the operation of machines due to the fact that corrosion could occur to effect precipitates and/or adhesive substances by their strong acidic carboxyl groups when they are brought into contact with non-ferrous metals, for example, copper-tin alloy, copper-zinc alloy and the like.
The organocarboxylic acid esters have a similar drawback by the fact that their ester bonds used to be cleaved by their hydrolysis due to moisture and heat derived from their environment to isolate carboxyl groups.
Further, these rust inhibitors often form precipitates and/or sludges by a chemical reaction when they are brought into contact with basic substances thereby becoming the origin of a trouble in case of being used jointly with basic additives or in the case of being used in ammonia compressor lubricants.
On the other hand, the organocarboxylic acid esters also form an acid by the hydrolysis of their ester bonds as mentioned above and the acid causes discoloring of a metal surface.
In addition to the above noted, they have lower demulsibility.
Inventors of the present invention arrived at the present invention as a result of serious efforts for developing a rust inhibitor not having the aforementioned drawbacks. In order to avoid the above drawbacks, three chemically neutral hydroxy groups, selected as polar groups, are combined with an oleophilic group of the rust inhibitor through an ether bond.